Gaza - Hamas forces launched a crackdown on supporters and charities linked to Palestinian President Mahmoud Abbas' Fatah movement in the Gaza Strip early Saturday after a mysterious blast that killed a number of Hamas people, Fatah sources said.

Among those detained by Hamas was a colonel working in the pro- Abbas intelligence service and a cameraman working for the German ARD television channel, the sources said.

A bomb planted under the car of a Hamas member went off late Friday, killing a girl and five members of Hamas' armed wing who were picnicking at the beach in the west of Gaza city.

The car was parked behind a tent used by a group of Hamas people. Dozens more people were reported wounded.

Hamas Islamists accuse Fatah of being behind a series of explosions in Hamas-controlled Gaza over the past 24 hours, but the secular movement says the blasts were a result of internal disputes among Hamas, which took over the Gaza Strip by force last year.

Fatah sources said Hamas police and the so-called internal security service arrested dozens of the movement's supporters and members in Gaza city and closed a number of charities after confiscating their documents and computers.

Ihab Nasser, director of the North Society for Social Development, said he was surprised to hear that police of the deposed government had broken into his organisation's offices.

"It is a non-profit society and has no thing to do with the political situation," Nasser said, adding that his organisation nowadays holds a UN-sponsored summer camp for children.

At dawn, members of the internal security service of Hamas broke into the house of Sawah Abu Saif, the ARD cameraman, seized his laptop and cellular phone and took him with them, his family said.

The crackdown comes after the interior ministry of the Hamas government said it opened an investigation into the explosion.

Hamas ousted the Fatah movement from Gaza in June 2007 after routing pro-Abbas forces. The Palestinian president fired a Hamas-led coalition and appointed a western-backed administration ruling from West Bank. (dpa)